1. Field Of The Invention
The present invention relates a wheeled transport device, and more particularly, a cart for transporting sensitive electronic circuit boards, components thereof, and computer tapes or the like, subject to electrical field damage, while providing protection against such damage during transit from one location to another.
2. Description Of The Prior Art
Electronic devices and circuit boards, such as those used by the telecommunication and electronic industries, contain expensive solid-state and microelectronic components which are extremely sensitive to electrical field damage, such as, electrostatic discharges from their ambient surroundings (ESD), electromagnetic interference (EMI), radio frequency interference (RFI), and electromagnetic pulses (EMP). Often, such devices can run in the thousands or tens of thousands of dollars each, yet can be destroyed; e.g., by transient static charges such as those which sometimes jump from a person's hand to a metal handrail or the like under conditions of low humidity. Such circuit boards can also be destroyed by the uncontrolled, rapid discharge of components thereon after removal of the boards from active service in a computer, switching system, or the like. It is therefore necessary to protect such circuit boards against electrical field damage as they are being transported from a storage or use location under ambient conditions.
Prior solutions to this problem has centered around containers for housing the circuit boards, components, or tapes, such as plactic bags or cartons, which are rendered conductive with an appropriate anti-static angent. Chemical agents for providing anti-static properties are disclosed, for example, in U.S. Pat. No. 3,405,001. It also has been common to handle and store circuit board modules in plastic barrier bags or plastic blocks such as "Styrofoam" which have been treated with such an anti-static chemical agent. Examples of known anti-static containers for electronic parts are provided in U.S. Pat. Nos. 4,293,070 and 4,231,901. The '070 patent discloses a container composed entirely of paperboard coated on the inside surfaces with conductive carbon black particles to prevent an outside static electricity charge from passing through the container. In the '901 patent, a urethane foam having electrically conductive properties is used to wrap electronic components to protect them from static charge. The foam contains a binding agent and is impregnated generally uniformly therethrough with an electrically conductive amount of an electrically conductive particulate material, e.g., carbon black, silver, aluminum or a metal salt. U.S. Pat. No. 4,223,368 discloses an electrostatic discharge protection device adapted to be clipped onto edge connectors of a circuit board assembly. The device includes a shunt for electrically short-circuiting the edge connectors of the board.
When removing circuit boards from electronic mainframes, it is inconvenient to repackage the boards in individual storage containers such as cartons or bags described above in order to transport them from one location to another. However, it is imperative, because of the expense of duplicating such a board that such boards be protected against electrical field damage as they are being transported from one location to another.
The present invention relates to a cart with a Faraday shielded container, i.e., one where electrical field charges will circulate about the container to ground, which can be used as a transport vehicle for such sensitive electronic boards so they will not be subject to electrical field damage from the ambient surroundings or from rapid electrostatic discharges from the board itself during transport.